The use of conventional gate electrode and gate dielectric materials is becoming increasingly problematic as feature sizes of semiconductor devices are continuing to be scaled to smaller dimensions. Among the problems encountered include increased resistance of the gate electrode, leakage of the gate dielectric, and polysilicon gate depletion effects. In an effort to overcome these problems, alternative materials are being investigated to replace conventional gate dielectric and gate electrode materials.
Refractory metals, refractory metal alloys, their nitrides, and aluminum are alternative materials currently being investigated for use as gate electrodes. These materials offer potential advantages over materials such as polysilicon because of their patternability, low sheet resistance, and scalability to advanced metal oxide semiconductor technologies. Among the refractory metals currently being considered include titanium, tantalum, tungsten, molybdenum, zirconium, or the like.
In selecting refractory metal materials for use as a gate electrode, a number of factors must be considered. Among these include the electrical, chemical, and physical properties of the refractory metal material. The selection process is further complicated because these properties can change as the refractory metal material is subjected to various thermal processing steps. Failure to compensate for these thermally induced changes can impact yield and potentially affect the reliability of the semiconductor device.